Methods and systems for operating aircraft landing gears

ABSTRACT

Methods and systems for performing landing gear operations. In one embodiment, a method for retracting a landing gear is useable with an aircraft having a gear door that at least partially covers a gear well when the landing gear is extended. The method can include receiving a first signal during movement of the aircraft down a runway for takeoff. The first signal can correspond to at least a first aspect of motion of the aircraft, such as upward rotation of the aircraft for liftoff. The gear door can be opened in response to receiving the first signal. The method can further include receiving a second signal after the aircraft has lifted off of the runway. The second signal can correspond to a second aspect of motion of the aircraft, such as the aircraft achieving a positive rate of climb. In response to receiving the second signal, the landing gear can be retracted into the gear well.

TECHNICAL FIELD

The following disclosure relates generally to aircraft landing gearsystems and, more particularly, to methods and systems for retractingaircraft landing gears.

BACKGROUND

Conventional jet transport aircraft typically include retractablelanding gears to reduce aerodynamic drag during flight. Such landinggears can extend downwardly from a wing or fuselage for landing andretract upwardly into corresponding gear wells for flight. Many aircraftalso include at least some form of gear door that closes over the gearwells when the landing gears are in the extended position. When closed,these gear well doors can protect systems within the gear wells fromforeign object damage during takeoff and landing, and can reduce noiseand drag. Throughout the following disclosure, unless otherwise noted,the term “gear doors” refers to gear well doors that at least partiallycover gear wells after extension of the corresponding landing gear.

When a conventional jet transport aircraft begins its takeoff roll, thegear doors are typically closed and remain in this position until afterliftoff. Under current practice, pilots wait until the aircraft hasachieved a positive rate of climb before initiating landing gearretraction. This usually occurs about three seconds after liftoff.Landing gear retraction typically begins with the opening of the geardoors to expose the gear wells. Next, the landing gears retract upwardlyinto the corresponding gear wells. When the landing gears are fullyretracted, or close to fully retracted, the gear doors begin closingbehind the landing gears to cover the gear wells for flight.

Retracting the landing gears quickly after liftoff can provide a numberof benefits. One benefit is the reduction in aerodynamic drag and thecorresponding increase in climb-rate that results from “cleaning up” theaircraft. Another benefit is the additional clearance that retractingthe landing gear can provide between the aircraft and ground obstaclesduring an obstacle-limited takeoff.

Conventional jet transport aircraft typically have hydraulically drivenlanding gear systems. On such aircraft, the demands of the landing gearsystem typically determines the size of the hydraulic system. One knownmethod for increasing the speed of landing gear retraction is toincrease the capacity of the hydraulic system. One downside to thisapproach, however, is the increased cost associated with a largerhydraulic system. A further downside is the reduction in aircraftperformance that results from the increased weight of a larger hydraulicsystem.

SUMMARY

The present invention is directed generally toward aircraft landing gearsystems and methods for retracting aircraft landing gears. A method inaccordance with one aspect of the invention is usable for retracting alanding gear of an aircraft during takeoff. The aircraft can include alanding gear well configured to receive the landing gear as the landinggear moves from an extended position to a retracted position. Theaircraft can further include at least one landing gear door moveablebetween a closed position and an open position. In the closed position,the landing gear door can at least partially cover the landing gearwell. In this embodiment, the method for retracting the landing gearincludes receiving a first signal during movement of the aircraft down arunway for takeoff. The first signal can correspond to at least a firstaspect of motion of the aircraft. In response to receiving the firstsignal, movement of the landing gear door from the closed position tothe open position is initiated.

Another aspect of this method includes receiving a second signal afterthe aircraft has lifted off of the runway. The second signal cancorrespond to at least a second aspect of motion of the aircraftdifferent from the first aspect of motion. In response to receiving thesecond signal, movement of the landing gear from the extended positionto the retracted position can be initiated.

In a particular aspect of this method, receiving the first signal duringmovement of the aircraft down the runway can include receiving a signalthat is automatically generated in response to the aircraft rotatingupwardly. In another aspect of this method, receiving a second signalafter the aircraft has lifted off of the runway can include receiving asignal associated with a control input manually generated by a pilot ofthe aircraft in response to the aircraft achieving a positive rate ofclimb.

An aircraft system configured in accordance with one aspect of theinvention includes a controller configured to be operably coupled to alanding gear door and a landing gear of an aircraft. The landing gearcan be moveable between an extended position and a retracted position.The landing gear door can be moveable between a closed position and anopen position. The controller can be configured to retract the landinggear by a method that includes receiving a first signal during movementof the aircraft down a runway for takeoff. The first signal cancorrespond to at least a first aspect of motion of the aircraft. Inresponse to receiving the first signal, movement of the landing geardoor from the closed position to the opened position is initiated. Themethod can further include receiving a second signal separate from thefirst signal after the aircraft has lifted off of the runway. The secondsignal can correspond to at least a second aspect of motion of theaircraft. In response to receiving the second signal, movement of thelanding gear from the extended position to the retracted position can beinitiated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bottom front isometric view of an aircraft having a landinggear system configured in accordance with an embodiment of theinvention.

FIG. 2 is an enlarged, partially schematic, front cross-sectional viewof a portion of the aircraft of FIG. 1 illustrating aspects of thelanding gear system configured in accordance with an embodiment of theinvention.

FIG. 3 illustrates a flow diagram of a routine for retracting a landinggear in accordance with an embodiment of the invention.

FIG. 4 is a graph that illustrates level-loading of a landing gearhydraulic system in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

The following disclosure describes methods and systems for retractingaircraft landing gears. Certain details are set forth in the followingdescription and in FIGS. 1-4 to provide a thorough understanding ofvarious embodiments of the invention. Other details describingwell-known structures and systems often associated with aircraft andaircraft landing gear systems are not set forth in the followingdisclosure to avoid unnecessarily obscuring the description of thevarious embodiments of the invention.

Many of the details, dimensions, angles, and other features shown in theFigures are merely illustrative of particular embodiments of theinvention. Accordingly, other embodiments can have other details,dimensions, and features without departing from the spirit or scope ofthe present invention. In addition, further embodiments of the inventionmay be practiced without several of the details described below.

In the Figures, identical reference numbers identify identical or atleast generally similar elements. To facilitate the discussion of anyparticular element, the most significant digit or digits of anyreference number refer to the Figure in which that element is firstintroduced. For example, element 110 is first introduced and discussedwith reference to FIG. 1.

FIG. 1 is a bottom front isometric view of an aircraft 100 having alanding gear system 110 configured in accordance with an embodiment ofthe invention. In one aspect of this embodiment, the aircraft 100includes a wing 104 extending outwardly from a fuselage 102. The landinggear system 110 can include a nose gear 112 extending downwardly from aforward portion of the fuselage 102, and two or more main gears 120(identified individually as a first main gear 120 a and a second maingear 120 b) extending downwardly from the wing 104. Each main gear 120can include a wheel truck 122 pivotally coupled to a main strut 124. Themain strut 124 can be pivotally attached to the wing 104 and configuredto retract inwardly and upwardly into a corresponding gear well 126. Inthe illustrated embodiment, the gear well 126 extends across a portionof the underside of the wing 104 and the fuselage 102.

In another aspect of this embodiment, the aircraft 100 further includesa first gear door 128 and a second gear door 129. The first gear door128 can be hingeably attached to the fuselage 102 and moveable between aclosed position (as illustrated in FIG. 1) and an open position (notshown). In the closed position, the first gear door 128 covers theportion of the gear well 126 that extends into the fuselage 102. In theopen position, the gear well 126 can receive the retracting main gear120. The second gear door 129 can be hingeably attached to the wing 104and coupled to the main gear 120 so that it moves in conjunction withthe main gear 120.

When the aircraft 100 begins moving down a runway for takeoff, the firstgear door 128 (“gear door 128”) is closed to protect systems within thefuselage portion of the gear well 126 from foreign object damage. Asdescribed in greater detail below, however, as the aircraft 100approaches liftoff speed and begins to rotate upwardly, the gear door128 starts to open. In this way, the gear door 128 can be fully open, orat least close to fully open, after liftoff when the pilot determinesthat the aircraft 100 has achieved a positive rate of climb and manuallyinitiates the gear retraction process. By opening the gear door 128 inadvance of the pilot initiating gear retraction, the overall time forgear retraction can be significantly reduced. In addition, as furtherdescribed in detail below, by dovetailing the door opening and gearretraction operations together in sequence, the demands on the aircrafthydraulic system (not shown) can be reduced, thereby enabling use of alighter and less expensive hydraulic system.

FIG. 2 is an enlarged, partially schematic, front cross-sectional viewof a portion of the aircraft 100 illustrating aspects of the landinggear system 110 configured in accordance with an embodiment of theinvention. In one aspect of this embodiment, the landing gear system 110includes a hydraulic gear actuator 241 (“gear actuator 241”) operablycoupled to the main gear 120, and a hydraulic door actuator 242 (“dooractuator 242”) operably coupled to the gear door 128. The gear actuator241 can include a first hydraulic fluid port 243 a (“first fluid port243 a”) and a second hydraulic fluid port 243 b (“second fluid port 243b”). The first fluid port 243 a and the second fluid port 243 b areconfigured to receive pressurized hydraulic fluid from a hydraulicsystem 240 (shown schematically) for retraction and extension,respectively, of the gear actuator 241. For example, for retraction ofthe gear actuator 241, pressurized hydraulic fluid flows into the firstfluid port 243 a from the hydraulic system 240 and drives a piston 261in a first direction causing it to retract. Conversely, for extension ofthe gear actuator 241, pressurized hydraulic fluid flows into the secondfluid port 243 b from the hydraulic system 240 and drives the piston 261in the opposite direction causing the gear actuator 241 to extend. Asthe piston 261 moves in either direction, low pressure hydraulic fluidreturns to the hydraulic system 240 via the fluid port 243 on the lowpressure side of the piston 261. Retraction of the gear actuator 241causes the main gear 120 to pivot upwardly about a trunnion 223 from anextended position 252 a to a retracted position 252 b. In the retractedposition, the main gear 120 is neatly stowed within the gear well 126.Conversely, extension of the gear actuator 241 causes the main gear 120to return to the extended position 252 a.

In another aspect of this embodiment, the gear actuator 241 furtherincludes a first snubber valve 245 a operably coupled to the first fluidport 243 a, and a second snubber valves 245 b operably coupled to thesecond fluid port 243 b. The snubber valves 245 can be eithermechanically or electrically actuated to restrict the flow of hydraulicfluid through the respective fluid ports 243 when the piston 261approaches either end of its stroke. Restricting the flow of hydraulicfluid in this manner slows (“snubs”) the piston 261 near the ends of itsstroke. Gradually slowing the piston 261 near the end of its stroke canprevent damage to the main gear 120 that might otherwise occur if themain gear 120 is rapidly driven into stops at either the extendedposition 252 a or the retracted position 252 b.

In a further aspect of this embodiment, the landing gear system 110additionally includes a position sensor 262 (shown schematically)operably coupled to the gear actuator 241. In one embodiment, theposition sensor 262 can be configured to detect when snubbing of thepiston 261 has begun during retraction of the gear actuator 241. Asdescribed in greater detail below, when snubbing of the piston 261begins, the demand placed on the hydraulic system 240 by the gearactuator 241 is gradually reduced. As a result, the hydraulic system 240can begin providing power to the door actuator 242 at this point in timewithout having to increase its output, i.e., by maintaining a levelhydraulic load. In one embodiment, the position sensor 262 can includean electrical device, such as an LVDT (linear variable displacementtransducer), to detect piston snubbing. In other embodiments, othertypes of devises, such as a simple mechanically operated switch, can beemployed for this purpose.

In yet another aspect of this embodiment, the door actuator 242 includesa first hydraulic fluid port 244 a and a second hydraulic fluid port 244b configured to receive pressurized hydraulic fluid from the hydraulicsystem 240 for closing and opening, respectively, the gear door 128. Forexample, pressurized hydraulic fluid flowing into the first fluid port244 a causes the door actuator 242 to retract. Conversely, pressurizedhydraulic fluid flowing into the second fluid port 244 b causes the dooractuator 242 to extend. Extension of the door actuator 242 causes thegear door 128 to open downwardly about a hinge-line 227 moving from aclosed position 254 a to an open position 254 b. Conversely, retractionof the door actuator 242 causes the gear door 128 to move in theopposite direction.

In a further aspect of this embodiment, the landing gear system 110additionally includes a controller 230 (shown schematically) operablycoupled to the hydraulic system 240. The controller 230 can beconfigured to receive input signals from a number of different sources,and then transmit corresponding control signals to the hydraulic system240 for operation of the main gear 120 and the gear door 128. Forexample, in one embodiment the controller 230 can receive manuallygenerated input signals from a cockpit gear selector 272 (shownschematically). In another embodiment, the controller 230 can receiveautomatically generated input signals from a nose gear sensor 274, awheel truck sensor 276, and/or an air speed sensor 278 (all shownschematically).

In yet another aspect of this embodiment, the nose gear sensor 274, thewheel truck sensor 276, and the air speed sensor 278 have otherarrangements and can be utilized to automatically transmit a signal tothe controller 230 when a particular aspect of aircraft motion indicatesthat the aircraft 100 is approaching liftoff during a takeoff roll. Forexample, the nose gear sensor 274 can be configured to automaticallytransmit a signal to the controller 230 when the weight on the nose gear112 (FIG. 1) decreases to a preselected amount. Alternatively, the wheeltruck sensor 276 can be configured to automatically transmit a signal tothe controller 230 when the wheel truck 122 rotates to a preselectedangle with respect to the main strut 124. The foregoing signalsgenerated by the nose gear sensor 274 and the wheel truck sensor 276 cancorrespond to the aircraft 100 rotating upwardly during its takeoff rolljust before liftoff. In yet another embodiment, the air speed sensor 278can be configured to automatically transmit a signal to the controller230 when the aircraft 100 reaches a preselected air speed correspondingto liftoff In other embodiments, other sensors can be used to provideother signals corresponding to liftoff. For example, in anotherembodiment, a main gear sensor can be included to provide a signal whenthe weight on the main gears 120 decreases to a preselected amount.

As the aircraft 100 is moving down a runway prior to takeoff, the maingear 120 is extended and the gear door 128 is closed as shown in FIG. 2.As the aircraft 100 builds up speed, one or more of the sensors 274, 276or 278 can automatically transmit a signal to the controller 230 whenthe aircraft 100 is just about to lift off the runway. As discussedabove, in one embodiment, this signal can be generated by the nose gearsensor 274 when the weight on the nose gear decreases to a preselectedamount. Alternatively, this signal can be generated by the wheel trucksensor 276 when the angle between the wheel truck 122 and the main strut124 reaches a preselected angle. In yet another embodiment, the signalthat the aircraft 100 is just about to lift off can be automaticallygenerated by the air speed sensor 278 when the air speed of the aircraft100 reaches liftoff speed. In other embodiments, other signals can beused to indicate that the aircraft 100 is just about to lift off of therunway. For example, in one other embodiment, an engine speed signal canbe used for this purpose. In a further embodiment, a weight sensorcoupled to one or both of the main gears 120 can be used for thispurpose. In yet another embodiment, an inclinometer mounted to theairframe can be used. Accordingly, in still further embodiments, othersignals can be transmitted to the controller 230 when the aircraft 100is at or near the point of lifting off of the runway.

When the controller 230 receives the signal indicating that the aircraft100 is just about to lift off, the controller 230 sends a correspondingcontrol signal to the hydraulic system 240 instructing the hydraulicsystem 240 to initiate opening of the gear door 128. The hydraulicsystem 240 responds by extending the door actuator 242 causing the geardoor 128 to open. Accordingly, the gear door 128 opens just before orduring liftoff of the aircraft 100, and before the pilot (not shown) hasmanually initiated landing gear retraction by operating the cockpit gearselector 272.

Once the pilot has determined that the aircraft 100 has achieved apositive rate of climb, the pilot initiates landing gear retraction bymanual operation of the cockpit gear selector 272. This event typicallyoccurs two to three seconds after the aircraft 100 has lifted off of therunway. At this point in time, the gear door 128 is fully open, or closeto fully open. As a result, when the pilot initiates landing gearretraction, the main gear 120 can immediately begin moving into the gearwell 126 without having to wait for the gear door 128 to open.

As the main gear 120 approaches the fully retracted position 252 b, thefirst snubber valve 245 a gradually restricts the flow of hydraulicfluid into the first fluid port 243 a, thereby slowing retraction of thefirst actuator 241. In a further aspect of this embodiment, the positionsensor 262 detects the start of actuator snubbing and transmits acorresponding signal to the controller 230. In response, the controller230 transmits a control signal to the hydraulic system 240 instructingthe hydraulic system to initiate movement of the gear door 128 from theopen position 254 b to the closed position 254 a. The hydraulic system240 responds by gradually increasing the flow of hydraulic fluid to thedoor actuator 242 causing the door actuator 242 to retract. In oneembodiment, this motion can be accomplished by a separate door controlvalve, or by an “easy-on” snubbing valve within the door actuator 242.By gradually increasing the flow of hydraulic fluid to the door actuator242 at the same rate as the flow of hydraulic fluid to the gear actuator241 is decreasing, the demand on the hydraulic system 240 is maintainedat an at least approximately constant level (i.e., the hydraulic system240 is “level-loaded”). Once the main gear 120 is fully retracted, thegear door 128 closes behind it.

One feature of aspects of the invention described above with referenceto FIG. 2 is that opening of the gear door 128 is automaticallyinitiated before the pilot initiates retraction of the main gear 120.One advantage of this feature is that the main gear 120 can beginretracting immediately, or almost immediately, after the pilot initiatesmain gear retraction. In contrast, conventional landing gear systems areconfigured to respond to the pilot's gear retraction command by firstopening the gear door 128, and then retracting the main gear 120. As aresult, conventional landing gear systems take significantly longer toretract the main gear 120 than the landing gear system 110 describedabove with reference to FIG. 2. A further feature of aspects of theinvention described above with reference to FIG. 2 is that the load onthe hydraulic system 240 can be maintained at an at least approximatelyconstant level during retraction of the main gear 120. This“level-loading” is achieved by gradually increasing the flow ofhydraulic fluid to the door actuator 242 for door closure as the flow ofhydraulic fluid to the gear actuator 241 for gear retraction isdecreasing. One advantage of this feature is that the hydraulic systemdoes not have to be sized to provide full power to both the dooractuator 242 and the gear actuator 241 at the same time.

FIG. 3 illustrates a flow diagram of a routine 300 for retracting anaircraft landing gear in accordance with an embodiment of the invention.In one aspect of this embodiment, the controller 230 of FIG. 2 caninclude a computer processor that implements the routine 300 inaccordance with instructions stored on a computer-readable medium. Inother embodiments, the routine 300 can be implemented by other aircraftsystems using other media. The routine 300 starts when the aircraft (notshown) begins moving down the runway for takeoff with the landing geardown and the corresponding gear door closed. In block 302, the routine300 receives a signal indicating that the aircraft has begun upwardrotation for liftoff. As discussed above with reference to FIG. 2, thissignal can be automatically generated when the load on the nose geardecreases to a preselected level, when the wheel truck reaches apreselected angle relative to the main gear strut, and/or when the airspeed of the aircraft reaches a preselected speed. In block 304, theroutine 300 initiates opening of the gear door in response to receivingthe signal in block 302.

In decision block 306, the routine 300 determines if it has received asignal from the pilot to retract the landing gear. In one embodiment, asdiscussed above, this signal can come from the pilot via actuation of acockpit gear selector. If the routine 300 has not received a signal toretract the landing gear, then the routine waits until such a signal isreceived. When the routine 300 does receive a signal to retract thelanding gear, the routine proceeds to decision block 312 to determine ifthe gear door is at least X % open. In one aspect of this embodiment, Xcan correspond to that percentage of door movement at which the geardoor is sufficiently open such that the landing gear can be safelyretracted without striking the gear door. For example, in oneembodiment, X % may need to be at least approximately 75% beforeinitiating landing gear retraction. In other embodiments, the percentageof door opening can vary depending on the particular landing gearconfiguration. If, in decision block 312, the gear door is not at leastX % open, then the routine 300 repeats until the gear door is at least X% open. Once the gear door is at least X % open, the routine proceeds toblock 314 and initiates retraction of the landing gear.

After initiating landing gear retraction, the routine 300 proceeds todecision block 316 and waits for the landing gear to be retracted atleast Y %. In one embodiment, Y % corresponds to that percentage oflanding gear retraction at which snubbing of the landing gear motionbegins. As discussed above with reference to FIG. 2, the onset oflanding gear snubbing can be detected with a mechanical orelectromechanical position sensor operably coupled to the landing gearactuator. In one embodiment, Y % can be at least approximately 90%. Inother embodiments, landing gear snubbing can occur at differentpercentages of landing gear motion depending on the particular landinggear configuration. If the landing gear is not at least Y % retracted,then the routine 300 repeats until the landing gear is at leastapproximately Y % retracted. Once the landing gear has been retracted tothe point at which snubbing begins, the routine 300 proceeds to block318 and initiates closure of the gear door. As discussed above, in oneembodiment, hydraulic power to the gear door actuator is graduallyincreased as hydraulic power to the landing gear actuator is graduallydecreased. After block 318, the routine 300 is complete.

Although one or more of the routines described above initiate opening ofthe landing gear door while the aircraft is still on the runway, inother embodiments, initiation of landing gear door opening can beginafter the aircraft has lifted off the runway. For example, in oneembodiment, a signal for gear door opening can be automaticallygenerated when there is no weight on the landing gear, or shortlythereafter, indicating that the aircraft has just lifted-off. In otherembodiments, other types of signals can be automatically or manuallygenerated to initiate gear door opening after the aircraft haslifted-off the runway. These signals can be generated in a differentmanner than the signal received to initiate landing gear retraction.

FIG. 4 is a graph 400 illustrating level-loading of a landing gearhydraulic system in accordance with an embodiment of the invention. Thegraph 400 includes a vertical axis 402 measuring hydraulic system flow,and a horizontal axis 404 measuring time. In one embodiment, the eventsillustrated by the graph 400 can correspond to the different landinggear retraction events described above with reference to FIGS. 1-3. Forpurposes of illustration, opening of the gear door begins with aircraftrotation at Time=T_(D). From this point, hydraulic system flow increasesrapidly from L=0 to level L=1. The hydraulic system flow maintains thislevel until the gear door is at least approximately fully open, at whichtime the flow to the gear door actuator decreases rapidly to at leastapproximately L=0.

In the illustrated embodiment, the pilot initiates retraction of thelanding gear at T_(G), which is about the same time the gear door isfully opened. As mentioned above, the pilot typically initiates gearretraction after the aircraft achieves a positive rate of climb. Whilethis can occur at about the same time the gear door is fully open (asillustrated in FIG. 4), in other embodiments, the pilot can initiatelanding gear retraction at other times, such as after the gear door isfully open or slightly before the gear door is fully open. When thepilot initiates landing gear retraction, the hydraulic flow increasesrapidly back up to the level L=1. The hydraulic system maintains thisflow level while the landing gear is retracting and until snubbing ofthe landing gear motion begins at T_(S). At T_(S), hydraulic flow to thelanding gear actuator for landing gear retraction begins to decrease. Atthe same time, hydraulic flow to the gear door actuator for closure ofthe gear door begins to increase. In this manner, the load on thehydraulic system is maintained at an at least approximately constantlevel. When the hydraulic flow to the landing gear actuator has stopped,the hydraulic flow to the gear door actuator is at the level L=1 andmaintains this level until snubbing of the gear door actuator begins, atwhich time hydraulic flow to the gear door actuator decreases down tothe level L=0.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1-40. (canceled)
 41. An aircraft system comprising: landing gear movablebetween an extended position and a retracted position, wherein thelanding gear is at least partially stowed in a gear well when thelanding gear is in the retracted position; a landing gear door movablebetween an open position and a closed position, wherein the landing geardoor at least partially covers the gear well when the landing gear dooris in the closed position; at least a first actuator operably coupled tothe landing gear and configured to move the landing gear between theextended position and the retracted position; at least a second actuatoroperably coupled to the landing gear door and configured to move thelanding gear door between the open position and the closed position; anda controller operably coupled to the first and second actuators, whereinthe controller causes the second actuator to open the gear door inresponse to a first signal, and wherein the controller further causesthe first actuator to retract the landing gear in response to a secondsignal different from the first signal.
 42. The aircraft system of claim41 wherein the controller causes the second actuator to open the geardoor in response to an automatically generated signal, and wherein thecontroller further causes the first actuator to retract the landing gearin response to a manually generated signal.
 43. The aircraft system ofclaim 41 wherein the controller causes the second actuator to open thegear door in response to a signal that is automatically generated by anaspect of aircraft motion, and wherein the controller further causes thefirst actuator to retract the landing gear in response to a signal thatis manually generated.
 44. The aircraft system of claim 41 wherein thecontroller causes the second actuator to open the gear door in responseto a signal that is automatically generated by aircraft rotation, andwherein the controller further causes the first actuator to retract thelanding gear in response to a signal that is manually generated when theaircraft achieves a positive rate of climb.
 45. The aircraft system ofclaim 41 wherein the first and second actuators are hydraulic actuators,wherein the aircraft system further comprises a hydraulic systemoperably coupled to the first and second actuators, and wherein thecontroller is operably coupled to the hydraulic system, the controllercausing the hydraulic system to move the second actuator and open thegear door in response to a first signal, the controller further causingthe hydraulic system to move the first actuator and retract the landinggear in response to a second signal different from the first signal. 46.The aircraft system of claim 45 wherein the controller level-loads thehydraulic system during retraction of the landing gear and closure ofthe gear door such that the flow of hydraulic fluid is maintained at orbelow an at least approximately constant level.
 47. An aircraftcomprising: a fuselage; a passenger cabin positioned in the fuselage; awing extending outwardly from the fuselage; a landing gear attached tothe wing, the landing gear being movable between an extended positionand a retracted position, wherein the landing gear is at least partiallystowed in a gear well when the landing gear is in the retractedposition; a landing gear door movable between an open position and aclosed position, wherein the landing gear door at least partially coversthe gear well when the landing gear door is in the closed position; atleast a first actuator operably coupled to the landing gear andconfigured to move the landing gear between the extended position andthe retracted position; at least a second actuator operably coupled tothe landing gear door and configured to move the landing gear doorbetween the open position and the closed position; and a controlleroperably coupled to the first and second actuators, wherein thecontroller causes the second actuator to open the gear door in responseto an automatically generated signal, and wherein the controller furthercauses the first actuator to retract the landing gear in response to amanually generated signal.
 48. The aircraft system of claim 47 whereinthe controller causes the second actuator to open the gear door inresponse to a signal that is automatically generated by an aspect ofaircraft motion.
 49. The aircraft system of claim 47 wherein thecontroller causes the second actuator to open the gear door in responseto a signal that is automatically generated by aircraft rotation. 50.The aircraft system of claim 47 wherein the controller causes the secondactuator to open the gear door in response to a signal that isautomatically generated when weight is lifted off of the landing gear.51. The aircraft system of claim 47 wherein the controller causes thefirst actuator to retract the landing gear in response to a signal thatis manually generated when the aircraft achieves a positive rate ofclimb.
 52. The aircraft system of claim 47 wherein the first and secondactuators are hydraulic actuators, wherein the aircraft system furthercomprises a hydraulic system operably coupled to the first and secondactuators, and wherein the controller is operably coupled to thehydraulic system, the controller causing the hydraulic system to movethe second actuator and open the gear door in response to a firstsignal, the controller further causing the hydraulic system to move thefirst actuator and retract the landing gear in response to a secondsignal different from the first signal.
 53. The aircraft system of claim52 wherein the controller level-loads the hydraulic system duringretraction of the landing gear and closure of the gear door such thatthe flow of hydraulic fluid is maintained at or below an at leastapproximately constant level.